Generally in the field of semiconductor integrated circuits, aluminum layers are used as connection layer(s). Indeed, aluminum is a very good current conductor, easy to deposit, even onto surfaces having uneven protrusions, easy to etch and relatively cheap. Those aluminum connection layers are ended with pads, generally square-shaped, positioned at the periphery of the integrated circuit chip for establishing a contact with external connections.
One is then faced with a problem since aluminum is highly oxidizable and often forms insulating intermetallic compounds with other conductive materials. Therefore, various contact technologies have been developed, wherein adapted multilayer conductive structures are first deposited onto the aluminum pads.
The problem is particularly critical when, onto those aluminum pads, one wishes to carry out conductive bosses such as the ones that are used for example in the process called TAB. According to this process, outer connection metallizations are formed onto a film that is analog to the cinematography films; metallization portions onto those films, or beams, being then applied against the bosses of the integrated circuit which appear through a window opened into the film so that those bosses are positioned in front of the extremities of the beams.
A conventional process according to the prior art for carrying out such bosses consists in uniformly depositing onto an integrated circuit, wherein apertures are made above the aluminum pads, a sputtering of TiW then of gold. Later, a layer of resin is uniformly deposited onto the chip and windows are opened at the locations of the pads. A thick gold plating (from 0.02 to 0.03 mm) is carried out. The resin is then etched and the layer of TiW+Au is removed by ionic etching at the locations other than those were the bosses are formed.
The TiW+Au deposit and suppression operations are particularly complex steps which require a costly equipment. Thus, generally, the manufacturers of semiconductor integrated circuits, who are not liable to frequently use projecting contacts (bosses), for example for TAB, instead of highly investing into the necessary equipment, sub-contract the boss manufacturing operations. This also involves a substantial increase of the integrated circuit cost.